ABSTRACT
An analytical method was proposed to determine the ultra-trace metal elements in high-purity tetramethylammonium hydroxide ( TMAH).A total of 12 kinds of ultra-trace metal elements in 25% ( w/w) high-purity TMAH aqueous solution were directly determined after simple dilution with ultrapure water by inductively coupled plasma tandem mass spectrometry ( ICP-MS/MS ).In MS/MS mode, the spectral interferences were eliminated by the reaction of target ions with O2 or NH3/He (1:9, V/V) in the collision/reaction cell ( CRC ) of the ICP-MS/MS.Cr, Mn, Ni and Mo were determined using the O2 mass shift method.Cd and Pb were analyZed based on the O2 on-mass method.Fe, Co, Cu and Zn were determined using the NH3/He mass shift method.Mg and Al were determined using the NH3/He on-mass.The detection limits for analytes were in the range of 0.3-57.2 ng/L.The spiked recoveries were in range of 92.0%-106.0%, and the relative standard deviations (RSDs) were less than or equal to 4.6%.The procedure was applied for determining ultra-trace metal elements in 25% high-purity TMAH aqueous solution.
ABSTRACT
A method of derivatization at injection port following three phase hollow fiber microextraction with tetramethylammonium hydroxide (TMAH) as a dual-function reagent, for the simultaneous determination of salicylic acid, p-hydroxybenzoic acid, cinnamic acid, vanillic acid, p-coumaric acid and ferulic acid in beers by gas chromatography was developed. Phenolic acids were extracted from aqueous samples to a thin layer of organic solvent ( hexyl acetate) phase impregnated into the pores of the hollow fiber wall, and then back extracted to an acceptor solution (TMAH) located inside the lumen of the hollow fiber. Upon injection, the phenolic acids were derivatized to their methyl esters in the GC injection port. Several parameters related to the derivatization and extraction efficiency were optimized. The optimized conditions were as follows: hexyl acetate was used as the extraction solvent, an aqueous solution of TMAH (5% W/ V) was used as the derivatization reagent and acceptor phase, the pH value of donor phase was 2. 0, the concentrations of NaCl was 25% W/ V, the stirring rate was 500 r/ min, the extraction time was 40 min. Under the optimal conditions, the linear range of phenolic acids was 0. 50 -15. 00 mg / L, the limits of detection were 0. 05 -0. 18 mg / L. The proposed method was applied to the determination of the phenolic acids in beers. Vanillic acid, p-coumaric acid and ferulic acid were found in the beer samples, others were not detected. The spiked average recoveries were 90. 1% -106. 8% and RSD% was less than 5. 9% (n =3). The method is suitable for the determination of phenolic acids in beers.